EP2329210B1 - Method for operating an oven - Google Patents

Description

The present invention relates to a method for operating a furnace, in particular a furnace for melting metal, such as scrap iron.

The melting of metals is one of the energy-intensive processes in which large amounts of energy must be used to achieve the desired result. Corresponding methods for operating a furnace are z. B. from the US 6,247,416 known. Due to the soaring costs of energy and the debate about carbon dioxide emissions, it is desirable to make the melting process of metals energetically more favorable.

On this basis, the present invention has for its object to provide a method for operating a furnace, in which the energy requirement to be used is reduced.

This object is achieved with the features of independent claim 1.

Dependent claims are directed to advantageous developments.

1. A) eine vorgebbare sprunghafte Reduktion des Brennstoffvolumenstroms auf einen Reduktionsvolumenstrom und
2. B) eine vorgebbare sprunghafte Erhöhung des Oxidansvolumenstroms auf einen Erhöhungsvolumenstrom
   erniedrigt und nach Ablauf der Reduktionsdauer in den Standardbetriebszustand zurückversetzt wird, wobei die Änderung des Volumenstroms mindestens 3% beträgt und verzögerungsfrei ist.

The inventive method for operating a furnace, in which a starting material comprising at least one metallic element is melted by the starting material is heated by at least one burner, which is operated with a fuel volume flow of a fuel and a Oxidansvolumenstrom an oxidant, wherein an exhaust gas temperature of the furnace in an exhaust gas line is monitored in at least one measuring point downstream of a post-combustion zone, wherein in a standard operating state the burner, a desired fuel volume flow and a Solloxidansvolumenstrom is supplied, wherein a change in the exhaust gas temperature in predeterminable time intervals and is compared with a predeterminable limit, characterized in that when the change in the exhaust gas temperature per unit time is greater than the limit value, the burner is placed for a reduction period in a reduction operating state in which the quotient of fuel flow to Oxidant flow rate by at least one of the following measures:

1. A) a predetermined jumpable reduction of the fuel volume flow to a reduction volume flow and
2. B) a predeterminable jump increase of the Oxidansvolumenstroms to an increasing volume flow
   is lowered and returned to the standard operating state at the end of the reduction period, wherein the change in the volume flow is at least 3% and is instantaneous.

An abrupt increase or reduction of a volume flow is understood to mean the delay-free change of the volume flow by at least 3%, preferably by at least 5%. So it is a sudden change to a discontinuous change in the manner of a jump. The change in the exhaust gas temperature is monitored by monitoring the exhaust gas temperature in a measuring point. By comparing the detected exhaust gas temperatures, the change in the exhaust gas temperature can be determined. The burner is preferably designed so that the flame of the burner strikes the starting material during operation and / or sweeps it over and / or sweeps it. The starting material usually comprises meltable metal and optionally additives such as, for example, coal and / or carbonaceous additives or compounds. A post-combustion zone is understood to mean a region in which afterburning of the exhaust gases can take place after leaving the furnace. In particular, such a post-combustion zone is downstream of a means for supplying air downstream of the furnace, which can be formed in particular as an air gap.

The metal to be melted may comprise, for example, scrap iron or aluminum. Other additives in the starting material are also impurities or by the nature of the goods to be melted contingent shares. For example. have to be melted beverage cans impurities in the form of paint or leftovers on. For example, engines have impurities in the form of lubricant or gear oil during melting. Many industrial goods have plastic components, components and / or coatings during melting.

Operation of the furnace will result in operating conditions where suddenly a greater amount of carbon or carbonaceous material will be available for oxidation. This is the case, for example, when melting metal in a rotary kiln with the addition of carbon and / or carbonaceous additives, such as coke and / or graphite or plastic parts when rotating the rotary kiln coal or carbon in larger quantities with the corresponding oxidant in Contact is coming. When melting, for example. Beverage cans or other coated or painted metallic objects it comes in contact with the oxidizing agent or upon reaching the corresponding flash point of the coating or coating for the oxidation of the corresponding coating or paint. On such occasions, due to the fuel volume flow and the oxidant volume flow, a situation arises in which a relatively large amount of carbon monoxide is produced. This is referred to below as carbon monoxide release. This carbon monoxide may further oxidize to carbon dioxide upon further contact with oxidant. This process is exothermic. In this carbon monoxide release and the subsequent oxidation of carbon monoxide to carbon dioxide, there is a significant, rapid increase in the temperature of the exhaust gas, since in the exhaust gas often ambient air for cooling the exhaust gas is supplied, further, the operating conditions of the furnace are not or only slightly changed. This is the case, for example, when the fuel supply, that is to say the fuel volume flow or the oxidant volume flow, is changed only slightly in small steps. Then there is a sharp increase in the exhaust gas temperature when Inkontaktreten with fresh air as so-called afterburning, for example. By 300 ° C or more. This is a rise in temperature, which is basically not available for melting the starting material, as it is in the exhaust system he follows. However, the increase in temperature leads to a greater load on the exhaust system, in particular of refractory linings thereof.

According to the present invention, the strong temperature rise in the exhaust gas, which occurs with a release of carbon monoxide, is detected and subsequently a predefinable sudden reduction of the fuel volume flow to a reduced volume flow is subsequently undertaken. This reduction volume flow differs significantly from the nominal fuel volume flow, for example by 10% or more. Thus, there is a sudden decrease in the supply of fuel, while the Oxidansvolumenstrom is kept constant. Further, since the carbon monoxide is oxidized, compared with the situation with a substantially constant fuel volume flow, a significant reduction in the exhaust gas temperature, which is still high due to the oxidation of the carbon monoxide release. As a result, the material of the exhaust pipe is less thermally stressed and thus has a longer service life.

Alternatively or additionally, the Oxidansvolumenstrom can be increased suddenly to a predetermined increase volume flow. As a result, the oxidation of the carbon monoxide release already targeted in the oven, so that a higher melting performance can be achieved. This makes the melting process more effective.

In principle, the reduction of the quotient of the fuel volume flow to the oxidant volume flow leads in an abrupt manner to a more effective process control with possibly lower load on the furnace material.

As fuel in particular organic compounds such as hydrocarbon, for example. Natural gas are used.

According to an advantageous embodiment of the method according to the invention, the limit value is selected so that the limit value is at least a factor of two, preferably at least three, greater than usual measured value fluctuations.

In this case, customary variations in measured values are understood to mean the usual scattering of the experimentally determined temperature values, as well as slight temperature changes not attributable to a release of carbon monoxide. By the factor of at least two between the limit value and the usual measured value fluctuations, it can be achieved that unintentional and unnecessary operation in the reduction operating state can be avoided.

According to a further advantageous embodiment of the method according to the invention, the limit value is selected such that it corresponds to the edge of a temperature rise due to carbon monoxide release in the furnace.

This means that the limit value is selected such that only when the temperature rises significantly does the operating state of the furnace change from the standard operating state to the reduction operating state.

According to a further advantageous embodiment, the limit value is at least 4 Kelvin / sec.

Particularly preferred is an embodiment in which the limit is at least 10 Kelvin / sec. lies. These strong, rapid increases in temperature can be attributed almost exclusively to carbon monoxide releases. Normal temperature increases due to the heating cycle and the measured value fluctuations are significantly lower. Consequently, a limit value of at least 5 Kelvin / sec. and in particular at least 10 Kelvin / sec. or even at least 20 Kelvin / sec. advantageous, since such a reliable detection of carbon monoxide release can be ensured.

According to a further advantageous embodiment of the method according to the invention, the reduction period is selected so that it corresponds to the duration of a temperature rise by carbon monoxide release in the oven.

In a given furnace both the duration and the level of temperature increases by carbon monoxide release are known or measurable, since these ovens are usually operated with certain compositions of starting materials so for example. Certain amounts of scrap iron and certain amounts of coal supplied. Therefore, this knowledge can be used to set both the limit value and the reduction duration and / or the reduction volume flow and / or the increase volume flow. Depending on the oven, this leads to the best possible reduction of the necessary energy input or a corresponding increase in the open efficiency.

According to a further advantageous embodiment of the method according to the invention, the reduction time is at least 20 sec.

Conventional carbon monoxide releases cause temperature increases, so-called peaks, which are at least 20 sec. Long. Therefore, by setting the reduction period to at least 20 sec., A reduction of the energy input can be achieved particularly advantageously.

According to a further advantageous embodiment of the method according to the invention, the reduction volume flow is so dimensioned that the difference between the desired fuel volume flow and reduction volume flow multiplied by the reduction duration corresponds to a fuel volume whose calorific value corresponds to the average calorific value of the oxidation of a carbon monoxide release to carbon dioxide in the furnace. Alternatively or additionally, increasing volume flow can be dimensioned so that a complete oxidation of the carbon monoxide release can take place.

The calorific value here means the amount of energy which is released thermally during the corresponding process. It is known, for example, that in the oxidation of 1 m ³ carbon monoxide to carbon dioxide an amount of energy of about 3.5 kWh (kilowatt hours) is released. Since the exhaust gas volume flow is usually known or can be determined by an exhaust gas analysis and also the usual carbon monoxide concentration in the exhaust gas is known or can be determined, can be calculated as how much carbon monoxide is converted in a carbon monoxide release to carbon dioxide. From this it can then be calculated how far the fuel input can be reduced. This is achieved by reducing the fuel volume flow and the reduction time. Alternatively or additionally, the increase volume flow can be dimensioned so that a complete oxidation of the carbon monoxide release can take place.

According to a further advantageous embodiment of the method according to the invention, the quotient of reduction volume flow and nominal fuel volume flow in the range of 0.3 to 0.9 and / or the quotient of Solloxidansvolumenstrom and increasing volume flow in the range of 0.3 to 0.9. These quotients advantageously allow a corresponding utilization of the thermal energy of the oxidation of the carbon monoxide release to carbon dioxide. It should be pointed out once again that there is a sudden reduction in the fuel volume flow and / or increase in the Oxidansvolumenstroms the transition from the desired operating condition in the reduction mode. Preference is given to a reduction of the fuel volume flow and / or an increase of the oxidant volume flow by 10 to 50%.

1. a) Luft und
2. b) Sauerstoff.

According to a further advantageous embodiment of the method according to the invention, the oxidant comprises at least one of the following substances:

1. a) air and
2. b) oxygen.

As oxidant so pure oxygen or ambient air, and mixtures thereof can be used. Preferred is an oxidant in which the oxygen content is up to 100%.

According to a further advantageous embodiment of the method according to the invention, the increasing volume flow is such that it is sufficient for the complete oxidation of a conventional carbon monoxide release.

Under known operating conditions also usually the carbon monoxide concentrations in carbon monoxide releases are known or measurable, so that an adjustment of the increase in volume flow can take place at a known reduction time.

According to a further advantageous embodiment, the starting material comprises carbon.

Here, the carbon can be present either in compounds as a paint, oil, grease, for example as a lubricating oil, transmission oil in the melting of engines or the like, or in pure form, for example in the form of anthracite.

1. a) Eisen;
2. b) Aluminium;
3. c) Mangan;
4. d) Zinn;
5. e) Zink; und
6. f) Blei.

According to a further advantageous embodiment of the method according to the invention, the starting material comprises at least one of the following metallic elements:

1. a) iron;
2. b) aluminum;
3. c) manganese;
4. d) tin;
5. e) zinc; and
6. f) lead.

The elements can occur in connections, especially in the recycling of industrial goods such as motors, batteries or solder. The method according to the invention can particularly preferably be used for melting iron scrap. Due to the high amount of energy required there, a high energy saving can be achieved by the method according to the invention due to the high melting point.

1. a) ein Rotationsofen;
2. b) ein Kupolofen;
3. c) ein Drehofen;
4. d) ein Kippofen;
5. e) ein Schmelz/Gießofen; und
6. f) ein Wannenofen.

According to a further advantageous embodiment of the method according to the invention, the furnace is an oven of one of the following types:

1. a) a rotary kiln;
2. b) a cupola furnace;
3. c) a rotary kiln;
4. d) a tilting furnace;
5. e) a melting / casting furnace; and
6. f) a furnace.

In particular, the use of the method according to the invention for operating a rotary kiln is advantageous because carbon monoxide emissions often occur due to the constant mixing of the starting material in the kiln during rotation. In the case of a cupola, for example, the release of carbon monoxide occurs when, after burning through a carbon layer, the starting material sags in the cupola.

1. a) der Sollbrennstoffvolumenstrom und
2. b) der Solloxidansvolumenstrom

in Abhängigkeit von der Temperaturänderung kontinuierlich verändert.According to a further advantageous embodiment of the method according to the invention, in the standard operating state, at least one of the following variables is obtained:

1. a) the desired fuel volume flow and
2. b) Solloxidansvolumenstrom

continuously changed depending on the temperature change.

This therefore occurs in situations where the change in temperature is below the threshold. In such operating states, a change in particular of the desired fuel volume flow by very small values, not abruptly on the reduction volume flow. The desired fuel volume flow and / or the Solloxidansvolumenstrom is thus continuously but not abruptly adaptable.

It is proposed an apparatus for carrying out the method according to the invention, comprising a control means which is suitable and intended for carrying out the method according to the invention and a temperature sensor for detecting the temperature of the exhaust gas of the furnace.

In a preferred embodiment of the device, an exhaust pipe is formed, with which the exhaust gas of the furnace can be removed, which has an angled portion, wherein the temperature sensor is formed downstream of the angled portion.

The angled section of the exhaust pipe prevents parts of the starting material, for example larger scrap parts, from reaching the temperature sensor and damaging it. Alternatively or additionally, the exhaust pipe may also have a portion with a slope, wherein the temperature sensor is preferably formed in a region which is increased compared to the furnace outlet, so as to achieve protection of the temperature sensor.

Fig. 1:

einen nach dem erfindungsgemäßen Verfahren betreibbaren Ofen;

Fig. 2:

einen Verlauf der Temperatur und des Kohlenmonoxidgehalts ohne Einsatz des erfindungsgemäßen Verfahrens;

Fig. 3:

einen Ausschnitt des Temperaturverlaufs ohne Einsatz des erfindungsgemäßen Verfahrens; und

Fig. 4

einen Ausschnitt des Temperaturverlaufs mit Einsatz des erfindungsgemäßen Verfahrens.

The details and advantages disclosed for the method according to the invention are applicable to the device and transferable and vice versa. In the following the invention will be explained in more detail with reference to the accompanying drawing, without being limited to the details and exemplary embodiments shown there. They show schematically:

Fig. 1:

a furnace operable by the process according to the invention;

Fig. 2:

a course of the temperature and the carbon monoxide content without the use of the method according to the invention;

3:

a section of the temperature profile without use of the method according to the invention; and

Fig. 4

a section of the temperature profile with use of the method according to the invention.

FIG. 1 schematically shows an embodiment of the device 1 according to the invention for operating a furnace 2. The furnace 2 is a rotary furnace in which at least one metallic element comprehensive starting material such as. Iron scrap is melted with additives such as coal. The furnace 2 comprises an inlet 3 with a burner 4. Through the burner 4, an oxidant such as oxygen, air or oxygen-enriched air and a fuel such as natural gas are introduced into the furnace 2. Furthermore, the furnace 2 comprises an outlet 5, through which the exhaust gases of the combustion and oxidation processes in the furnace 2 are transferred into an exhaust pipe 6. The exhaust pipe 6 comprises an angled portion 7, which is connected via a bent portion 8 with a straight portion 9. Via a suction device 10, the exhaust gas from the furnace 2 can be sucked through the exhaust pipe 6. Here, filter means 11 may be formed in the exhaust pipe 6, which effect a filtering and / or at least partially chemical reaction of the exhaust gas. Specifically, the bent portion 8 of the exhaust pipe 6 and the inside of the furnace 2 (not shown here) are lined with a refractory material 12 to achieve a resistance to the high temperature of the exhaust gas, the molten metal and the resulting slag.

The inlet region 13 of the straight section 9 is widened, its inner diameter being larger than the corresponding outlet 5 of the furnace 2. Furthermore, the inlet region 13 is formed at a distance 14 spaced from the outlet 5 of the furnace 2. By this distance 14, which serves as an air gap, ambient air 15 can be mixed with the exhaust gas, whereby it is cooled. The entering ambient air 15 can lead to the oxidation of carbon monoxide to carbon dioxide, so that the distance 14 serves as a means for supplying air. This oxidation of carbon monoxide to carbon dioxide is called post-combustion. This can take place in the afterburning zone 27 if the corresponding reaction conditions are present.

The device 1 comprises a temperature sensor 16 for determining the temperature of the exhaust gas of the furnace 2. This temperature sensor 16 is formed at a measuring point 17 in the exhaust pipe downstream of an afterburning zone 27 in the angled portion 7 of the exhaust pipe 6, that is, downstream of the bent portion 8 , The temperature sensor 16 is connected via a data line 18 to a control means 19. In the control means 19, the fuel volume flow is controlled via a fuel line 20 and the Oxidansvolumenstrom via an oxidant 21 to the burner 4. The control means 19 detects the temperature of the exhaust gas at the measuring point 17. This temperature is recorded at predeterminable time intervals, the recorded temperature values are compared with each other and the temporal change of the temperature is calculated. The measuring point 17 is formed downstream of the afterburning zone 27 of the exhaust pipe 6, in which an afterburning can take place, if the corresponding reaction conditions are present, in particular if carbon monoxide is present in the exhaust gas, which can react with atmospheric oxygen, which can enter through the air gap forming a distance 14 ,

If the change in temperature exceeds a predeterminable limit value, for example 5 ° C./sec., The furnace 2 is put into a reduction operating state. This means that the fuel volume flow is abruptly reduced from a desired fuel volume flow to a reduction volume flow, that is, the reduction volume flow is at least 5% below the desired fuel volume flow, preferably even at least 10% below the desired fuel volume flow. The reduction operating state is maintained for a predefinable reduction period. During this reduction period no further changes in the fuel volume flow are made, this remains constant.

The duration and the difference between the desired fuel volume flow and the reduction volume flow are such that they correspond to a reduced fuel supply in a calorific value of the order of magnitude that carbon monoxide release in the furnace 2 contributes to the energy introduced into the furnace. An increase in the Oxidansvolumenstrom is not necessary, since the direct consumption of the oxidant decreases due to the reduced fuel supply and so still available oxidizing agent such as. Oxygen can be used for the oxidation of carbon monoxide to carbon dioxide. The resulting thermal energy is used to further heat the starting material in the furnace 2.

The carbon monoxide releases occur whenever larger amounts of carbonaceous material such as coal come in contact with a sufficiently large amount of oxidant and / or reach a corresponding flame temperature. This may be the case, for example, in a rotary kiln, when iron scrap is melted with coal, such as anthracite coal, and larger amounts of coal come into contact with the oxidant as the kiln 2 is rotated. Then carbon monoxide is released from unoxidized carbon. This carbon monoxide release is further oxidized by contact with oxidant at a correspondingly high temperature to carbon dioxide. This process is exothermic. Without withdrawal of the fuel supply, there is a sharp increase in the temperature of the exhaust gas, often several hundred ° C, for example. By 350 ° C and more. This heating of the exhaust gas and consequently of the starting material in the furnace and the furnace is undesirable, that it is not necessary for melting the starting material and means a high thermal load on the furnace and in particular its inner wall and the exhaust pipe 6. Due to the process control according to the invention, this temperature rise is now significantly reduced. On the one hand, this leads to a considerable energy saving by saving fuel and, on the other hand, to a significantly lower thermal load on the furnace 2 and the exhaust gas line 6. The filter medium 11 is also exposed to a lower thermal stress.

FIG. 2 shows an experimentally determined temperature profile 22 of the exhaust gas temperature and an experimentally determined carbon monoxide path 23 of the carbon monoxide content in the exhaust gas of a rotary furnace. It can be seen that whenever the carbon monoxide curve 23 increases, so does the Temperature curve 22 increases. By carbon monoxide release 24 is meant a corresponding peak in the carbon monoxide pathway 23. Experimental measurements have shown that a corresponding peak in the course of the carbon monoxide practically corresponds at the same time to a corresponding peak in the corresponding temperature curve 22.

FIG. 3 schematically shows a section of the temperature profile 22 from FIG. 2 , The temperature profile 22 shows a steep rise. When compared with the predeterminable limit value 25, it is determined that the change 26 of the temperature is greater than the predetermined limit value 25. In this case, the furnace 2 is set from the standard operating state to the reduction operating state, if it is not already in the reduction operating state. After the predetermined reduction period, the furnace 2 is operated again in the standard operating condition.

Fig. 4 shows a corresponding temperature profile 22 in the exhaust gas using the method according to the invention. The carbon monoxide releases lead to a significantly reduced temperature increase, the thermal energy of the oxidation of carbon monoxide to carbon dioxide is better utilized. The carbon monoxide course 23 in the exhaust gas shows significantly lower peaks.

The inventive method and apparatus advantageously allow the operation of a furnace 2 for melting, for example. Of scrap iron with high energy savings potential compared to known from the prior art method, since a sudden and significant reduction of the fuel flow occurs when a strong change the temperature indicative of release and further reaction of a significant amount of carbon monoxide occurs. Thus, the heat generated in the combustion of carbon monoxide to carbon dioxide can be used for further heating of the starting material. Furthermore, the thermal loads of the furnace 2 and the exhaust pipe 6 are reduced in an advantageous manner and thus increases the service life of these devices.

LIST OF REFERENCE NUMBERS

1

Apparatus for operating a furnace

2

oven

3

inlet

4

burner

5

outlet

6

exhaust pipe

7

angled section

8th

curved section

9

straight section

10

suction

11

filter means

12

refractory material

13

inlet area

14

distance

15

ambient air

16

Temperature sensor

17

measuring point

18

data line

19

control means

20

fuel line

21

Oxidansleitung

22

temperature curve

23

carbon monoxide history

24

Carbon monoxide release

25

limit

26

Change of temperature

27

reburn

Claims (11)

1. Method for operating a furnace (2), wherein a starting material comprising at least one metal element is molten, wherein the starting material is heated by at least one burner (4) that is operated with a volumetric fuel flow of a fuel and a volumetric oxidant flow of an oxidant, wherein an exhaust gas temperature of the furnace (2) is monitored in an exhaust gas line (6) at least at one measuring point (17) downstream of a post combustion zone, wherein in a standard operating state a target volumetric fuel flow and a target volumetric oxidant flow is fed to the burner (4), wherein a change (26) of the exhaust gas temperature is recorded at predeterminable time intervals and is compared to a predeterminable threshold value (25), characterised in that when the change (26) of the exhaust gas temperature per unit time is greater than the threshold value (25), the burner (4) is put into a reduction operating state for a predetermined reduction period, wherein the ratio of volumetric fuel flow to volumetric oxidant flow is lowered by at least one of the following actions:

   A) a predeterminable sudden reduction of the volumetric fuel flow to a reduced volumetric flow and

   B) a predeterminable sudden increase of the volumetric oxidant flow to an increased volumetric flow,
   said ratio being reset to the standard operating state after expiry of the reduction period, wherein the change of the volumetric flow has a value of at least 3% and is instantaneous.
2. Method according to claim 1, wherein the threshold value (25) is selected so as to be greater than the usual measured value fluctuations by at least a factor of two.
3. Method according to one of the preceding claims, wherein the threshold value (25) is selected so as to correspond with the slope of a temperature increase due to carbon monoxide release in the furnace (2).
4. Method according to one of the preceding claims, wherein the threshold value (25) is at least 4 K/s.
5. Method according to one of the preceding claims, wherein the reduction period is selected so as to correspond with the period of a temperature increase due to carbon monoxide release in the furnace (2).
6. Method according to one of the preceding claims, wherein the reduction period is at least 20 seconds.
7. Method according to one of the preceding claims, wherein a ratio of the reduced volumetric flow and target volumetric fuel flow and/or the ratio of target volumetric oxidant flow and increased volumetric flow is in the region of 0.3 to 0.9.
8. Method according to one of the preceding claims, wherein the starting material comprises carbon.
9. Method according to one of the preceding claims, wherein the starting material comprises at least one of the following metallic elements:

   a) iron;

   b) aluminium;

   c) manganese;

   d) tin;

   e) zinc; and

   f) lead.
10. Method according to one of the preceding claims, wherein the furnace (2) is a furnace (2) of one of the following types:

    a) a rotary furnace;

    b) a cupola furnace;

    c) a rotary kiln;

    d) a tilting furnace;

    e) a smelting/casting furnace; and

    f) a tank furnace.
11. Method according to one of the preceding claims, wherein, in the standard operating state, at least one of the following variables:

    a) the target volumetric fuel flow and

    b) the target volumetric oxidant flow
    is continuously changed depending on the change in temperature.

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